ANTIMONY-STABILIZED GAAS(001)(2X4) RECONSTRUCTIONS

Structural and electronic properties of the Sb-stabilized GaAs(001)(2x 4) reconstructions are studied by means of first-principles pseudopote ntial calculations. Six structural models with Sb coverages of Theta = 3/4,1/2, and 1/4 are considered. The atomic geometries are optimized by means of total-energy calculations. Models with one or two Sb dimer s in the first atomic layer describe the stable surface depending on t he chemical potentials of the surface constituents. The model widely a ccepted so far, containing three dimers in the outermost layer, is unf avorable from the energetical point of view. The lengths of the Sb dim ers are about 2.9 Angstrom, in close agreement with recent x-ray stand ing-wave measurements. The surface electronic structures are similar t o those of As-rich GaAs(001) surfaces and dominated by filled Sb-dimer states and empty Ga dangling bonds close to the GaAs valence- and con duction-band edges, respectively.